Multiprotocol label switching is a standardized multi-layer switching technology that integrates Internet Protocol (“IP”) Layer 3 routing services with Layer 2 data forwarding based on label swapping. That is, MPLS uses labels to route packets through a network instead of using IP addresses. MPLS networks are gaining in popularity and strategic importance for enterprise and public network infrastructures, in part, because MPLS simplifies and improves data exchange while maintaining operability with legacy network technologies. In particular, MPLS works with various types of Layer 2 protocol data units (“PDUs”).
ATM is a technology for transmitting data that is broken down into equal sized data units called “cells.” Like MPLS, ATM is a connection-oriented technology based on VCs. Thus, MPLS can be used to communicate ATM cells using VCs based on a label in headers of ATM cells. ATM cells, however, must first be encapsulated into packets for transport through a MPLS network. This allows ATM networks to be bridged by an MPLS network to transport ATM cells between ATM networks.
To bridge two ATM networks together with an MPLS network, the MPLS network typically includes an ingress label switching router (“LSR”) and an egress LSR. The ingress LSR receives ATM cells from an ATM network and encapsulates the cells to form MPLS packets for transport over the MPLS network. The egress LSR receives the MPLS packets and reverses the result of the original encapsulation before forwarding the resulting ATM cells to another ATM network. This type of encapsulation process, which enables one network to send its data over another network connection, is referred to as a “tunnel”. To encapsulate an ATM cell for transport over an MPLS tunnel, a tunnel label and VC label are required. The tunnel label contains information used by LSRs to forward the MPLS packet through the tunnel. The VC label is used to distinguish emulated VCs, or label switched paths, within a single tunnel and to distinguish the different ATM VCs available at the egress LSR.
Before the ingress LSR can encapsulate an ATM cell to form an MPLS packet, the ingress LSR and the egress LSR must agree on the meaning of each label. For example, the ingress LSR must populate its routing table with label and route information for routing an incoming ATM cell across the MPLS network to the egress LSR. Furthermore, the ingress LSR must populate its routing table with the available routes, and the labels corresponding to those routes, on which the egress LSR can forward ATM cells. In prior schemes, this is generally accomplished by having the ingress and egress LSRs exchange and maintain route and label information by negotiating via a series of communication sessions, using a label distribution protocol (“LDP”). Such an exchange is explained in detail with reference to FIG. 1.
FIG. 1 illustrates a diagram of a prior art MPLS network environment bridging ATM networks with an ingress and egress LSRs that negotiate VC labels over a LDP session. Referring to FIG. 1, MPLS network environment 100 includes an ATM network 105 and ATM network 110 bridged by an MPLS network 101. An interface point, or switching node, between ATM network 105 and MPLS network 101 is represented by ingress LSR 115. Similarly, egress LSR 120 serves as an interface point between ATM network 110 and MPLS network 101. Ingress LSR 115 communicates with egress LSR 120 via tunnel 125.
To establish tunnel 125, a network administrator will manually configure ingress LSR 115 and egress LSR 120 to be used by Private Network to Network Interface (“PNNI”) protocols to communicate with ATM networks 105 and 110, respectively. Next, the network administrator will use a network management system (not shown) to identify the ingress and egress LSRs, 115 and 120. Ingress LSR 115 and egress LSR 120 initiate LDP sessions 130 through which they use standard IP protocols and peer discovery routines to determine one or more VCs through tunnel 125. Once the VCs have been determined, egress LSR 120 will initiate a series of LDP sessions 130 to negotiate common tunnel labels and VC labels for the label switched paths (LSP) through the tunnel 125, and to inform ingress LSR 115 about the labels associated with the paths to ATM nodes 140, 145, 150 and 155. The tunnel 125 is associated with a tunnel identification key or tunnel key. The tunnel key is a number that ranges, for example, from 0 to 4,294,96,295. The tunnel key must be the same at both ends of the tunnel.
One problem with such a prior art scheme is that it is not scalable. For example, in an extremely large MPLS WAN, there may be several LSR nodes between the ingress and egress LSRs as well as several ATM nodes connected at either edge. Thus, in order to negotiate VC labels, each node requires a separate label distribution session thereby placing a heavy processing burden on an LSR with multiple connections. Furthermore, the control and signaling sessions are in-band thereby lowering the bandwidth available for data transmissions.
Another problem with such a prior art scheme is that PNNI is incompatible with LDP, which is the protocol that performs the same functions in an MPLS network as PNNI. Consequently, a network administrator must perform time consuming and tedious tasks of manually configuring routing tables on one or more of the switching network nodes so that the ATM and MPLS networks work seamlessly. Furthermore, ATM nodes and the MPLS nodes tend to be manufactured from different vendors and have different network management systems creating further challenges.